Python bindings proof of concept

[tebeka]

We'd like to be able to use carrow from Python. A proof of concept is:

• Create sub directory for Python bindings
• Create a Python extension module that uses carrow. It should expose only one function build() that will return a pyarrow.Table
  • build can re-use the code in example_test.go
• Convert the returned table to a pandas.DataFrame

[tebeka]

There are several ways to create Python extension, IMO it's best to use Cython since it's what's pyarrow is using.

We'll probably need to change the C++ API we currently have to return a shared_ptr<Table> and then (un)wrap_table, see here.